The present invention relates to an optical disc apparatus for recording a light signal onto and reproducing it from an optical recording medium and to an optical pickup used in the optical disc apparatus.
An optical pickup which records information onto and reproduces it from an optical recording medium, such as a CD-R, a DVD±R, or a DVD-RAM, capable of being used for both a recording operation and a reproducing operation is available.
Such an optical pickup performs a recording and/or a reproducing operation by forming a light beam emitted from a light source into a parallel light beam by a collimator lens and irradiating the optical recording medium with the parallel light beam by an objective lens.
However, in such an optical pickup, aberration caused by variations in the characteristics of an optical element (optical component) in an optical system including a light source and an objective lens, or aberration caused by variations in the thickness of an optical recording medium, or aberration caused by differences in the locations of recording layers of a two-layer optical recording medium occurs.
Such aberrations have a great influence on the characteristics of a recording signal that is recorded onto an optical recording medium or on the characteristics of a reproduction signal that is reproduced from the optical recording medium. Therefore, for example, a proposal has been made to correct the aberrations by an aberration correcting device that is disposed in an optical system of an optical pickup and that includes a liquid crystal element (refer to Japanese Unexamined Patent Application Publication No. 2004-71081).
In the above-described related optical pickup, the aberration correcting device is disposed in an optical path connecting a collimator lens and an objective lens, that is, in the optical path in which a parallel light beam travels.
In reducing the size of the optical pickup, it is important to reduce the distance between the collimator lens and the objective lens. When the aberration correcting device is disposed between the collimator lens and the objective lens, clearances are typically provided between the aberration correcting device and the collimator lens that are adjacent each other and between the aberration correcting device and the objective lens that are adjacent each other in order to prevent interference (such as thermal expansion) therebetween. Therefore, such an optical pickup is disadvantageous from the viewpoint of reducing size.
In addition, the aberration correcting device itself has aberrations. Such aberrations tend to occur, the larger the effective diameter of a light beam passing through the aberration correcting device, that is, the larger the aberration correcting device. Therefore, the larger the aberration correcting device, the greater the costs for restricting such aberrations.
It is desirable to provide an optical pickup and an optical disc apparatus which are advantageous from the viewpoints of reducing size while reducing aberration and reducing costs.